PR 13128: Modify unprivileged mode infrastructure to support a multi-privilege design

PR 13128: Modify unprivileged mode infrastructure to support a multi-privilege design

vs the previous boolean privileged/unprivileged design.

- in stap
  - Store the specified privilege level as an enum as opposed to a boolean
  - Test privilege levels against the proper enumerator.
- in the generated code
  - Generate STP_PRIVILEGE macro with the specified privilege level
  - Generated code tests it against the proper privilege level.